Clinical characteristics and treatments of cap polyposis: a single center case series

Results Clinical characteristics There were 14 adult patients diagnosed with cap polyposis (Table 1), including 11 males and 3 females, with a median age of 58 years (range, 20–69 years). Common symptoms included hematochezia (7/14, 50%), diarrhea (6/14, 42.9%), and mucus stool (4/ 14, 28.6%). One patient (7.1%) had a history of ulcerative colitis and one patient (7.1%) had a history of rectal cancer treated by surgical operation. Four patients (28.6%) had no symptoms.


Introduction
Cap polyposis is a rare benign disease of the digestive tract, characterized by inflammatory polyps with a cap of inflammatory granulation tissue. First described in 1985 by Williams et al. [1], cap polyposis is now still introduced in case reports. The clinical course and pathogenesis of this disease are yet to be elucidated and specific therapies have not been established.

Patients and methods
In this study, we reported 14 patients with cap polyposis confirmed by endoscopy and pathology between January 2013 and December 2020 in Beijing Friendship Hospital, Capital Medical University (Beijing, China). The demographics, clinical manifestations, endoscopic and histopathological features, treatments, and outcomes of these cases were retrospectively analyzed.

Endoscopic features and histology
All patients underwent colonoscopy with findings of polyps. The endoscopic manifestations were polyps covered by a thick layer of white fibrinopurulent exudates. The polyps were most commonly located in the rectum only (10/14, 71.4%), in the sigmoid colon and the rectum (2/14, 14.3%), in the sigmoid colon only (1/ 14, 7.1%), and from the transverse colon to the rectum (1/14, 7.1%). The number of polyps ranged from one to several dozen.
Four patients (28.6%) had only one polyp, two patients (14.3%) had two polyps, and eight patients (57.1%) had three or more polyps on colonoscopy. The Paris classification of the polyps was as follows: sessile (Is) in nine patients (64.3%), subpedunculated (Isp) in one patient (7.1%), pedunculated (Ip) in one patient (7.1%), Is and Isp in two patients (14.3%), and Isp and Ip in one patient (7.1%). A 23-year-old male patient with multiple Is rectal polyps was misdiagnosed with rectal cancer in another hospital but no malignant evidence was found pathologically.
Pathologic examination showed polypoid tissue exhibiting elongated, dilated, or tortuous hyperplastic colonic crypts in their central parts and covered in superficial regions by a "cap" of inflamed and ulcerated granulation tissue, fibrin, and inflammatory exudate.

Management
The patients were treated with endoscopic mucosal resection (EMR), surgery, mesalazine, Hp eradication, and steroids alone or in combination. Eleven patients had EMR alone (four patients) or with medication (seven patients), two patients had surgical operation, and one patient was treated with medication (topical mesalazine and Hp eradication). All the four Hp-positive patients succeeded in eradiation.

Follow-up results
All the patients were followed up. The median time of follow-up was 26.5 months (range, 6-79 months). EMR was effective for most patients: 10 patients were asymptomatic after EMR, of whom 6 patients significantly improved on colonoscopy (polyps of <0.6 cm that did not need to be treated were found in three patients and no cap polyposis occurred in the remaining three patients); 4 asymptomatic patients did not undergo a second colonoscopy after EMR. The patient with widespread colon involvement remained troubled by abdominal pain and diarrhea after oral and topical mesalazine, oral prednisone with a starting dose of 40 mg, Hp eradication despite a negative testing result and three procedures of EMR, and the repeated colonoscopy showed no improvement. One surgical patient had multiple rectal polyps on colonoscopy a year after surgery and the other surgical patient had no recurrence 3 years later. The patient who received medication remained with mild diarrhea and hematochezia.

Discussion
In our series, the male gender predominated in cap polyposis and patients of a wide range of ages could be affected. Brunner et al. [2] found that cap polyposis could occur at any age and the youngest affected patient was aged 11 months. Cap polyposis predominantly affected the rectum and the sigmoid colon, occasionally other parts of the colon. The stomach could also be a target [3,4]. However, none of the patients showed gastric involvement in our series.
As for the treatments, EMR was effective for most patients. Only in one patient with an extensive involvement of the colon did it turn out to be ineffective. Since it is less invasive, EMR should be recommended for most patients with rectosigmoid involvement, especially for those with few polyps. Endoscopic submucosal dissection (ESD) was also reported to be successful in an intractable cap polyposis with rectosigmoid involvement [5]. ESD might be a treatment option for cases that are refractory to conservative treatments.
Since Oiya et al. [3] reported a case of cap polyposis treated successfully by the eradication of Hp, Hp infection has been suggested to play a role in cap polyposis. However, in our study, none of the Hp-positive patients resolved after successful Hp eradication. Therefore, the role of Hp in cap polyposis is not certain and it remains to be elucidated who will benefit from Hp eradication.
Besides Hp eradication, several other medical treatments, including aminosalicylates, antibiotics, steroids, and infliximab [6,7], have been reported with variable clinical outcomes. In our study, few patients used aminosalicylates, antibiotics, or steroids, and none of them showed a definite effect.
For the refractory patients, especially those with extensive involvement of the colon, surgical resection may be indicated. Two of our patients chose surgery, of whom one had recurrence a year after surgery and the other remained resolved >3 years after surgery.
From our study, the long-term prognosis was relatively good for most patients. However, there were still a small number of patients who were troubled by intractable symptoms, which greatly affected their quality of life.
To our knowledge, this is the largest case series in a single center. However, as a retrospective study, it still has some limitations. First, the number of cases is still too small to adequately evaluate the roles of different drug therapies including Hp eradication therapy. Second, for the refractory cases, we have not found any effective treatment besides surgery.
In conclusion, we reported 14 cases of benign cap polyposis and found that EMR has a definite treatment effect and should be the first choice if necessary. Surgical resection may be considered if medical and endoscopic therapy does not work.